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    <title>Document</title>
    <script src="./js/08-then方法优化.js"></script>
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    <script>
        let p = new Promise((resolve, reject)=>{
            resolve('ok');
        })
        let res = p.then(value=>{
            return new Promise((resolve,reject)=>{
                // setTimeout(()=>{
                //     reject('error');
                // },2000);
                resolve('test fn');
            })
            // 3. throw 123  ==> reject
            // return 123;
        })
        console.log(res);
    </script>
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